TYPES OF CONDUCTORS IN POWER TRANSMISSION SYSTEM

TYPES OF CONDUCTORS IN POWER TRANSMISSION SYSTEM

Symbols identifying different types of aluminum conductors are as follows:

AAC- All Aluminum Conductors.
AAAC- All Aluminum Alloy Conductors.
ACSR- Aluminum Conductor Steel Reinforced.

HTLS- High Temperature Low Sag.

In the early days of the transmission of electric power conductors were usually copper, but aluminum conductors have completely replaced copper for overhead lines because of the much lower cost and lighter weight of an aluminum conductor compared with a copper conductor of the same resistance. The fact that an aluminum conductor has a larger diameter than a copper conductor of the same resistance is also an advantage. With a larger diameter, the lines of electric flux originating on the conductor will be farther apart at the conductor surface for the same voltage. This means there is a lower voltage gradient at the conductor surface and less tendency to ionize the air around the conductor.
Ionization produces the undesirable effect called corona.

Aluminum-alloy conductors have higher tensile strength than the ordinary electrical-conductor grade of aluminum. ACSR consists of a central core of steel strands surrounded by layers of aluminum strands. ACAR has a central core of higher-strength aluminum surrounded by layers of electrical conductor grad e aluminum.
Alternate layers of wire of a stranded conductor are spiraled in opposite directions to prevent unwinding and to make the outer radius of one layer coincide with the inner radius of the next layer. Stranding provides flexibility for a large cross-sectional area. The number of strands depends on the number of layers and on whether all the strands are of the same diameter. The total number of strands in concentrically stranded cables, where the total annular space is filled with strands of uniform diameter is 7, 1 9, 37, 61, 91, or more.
Figure shows the cross section of a typical steel-reinforced aluminum cable (ACSR). The conductor shown has 7 steel strands forming a central core, around which there are two layers of aluminum strands. There are 24 aluminum strands in the two outer layers. The conductor stranding is specified as 24 Al/7 St, or simply 24/7. Various tensile strengths, current capacities, and conductor sizes are obtained by using different combinations of steel and aluminum.

TECHNICAL PARTICULARS OF ACSR 'PANTHER', 'ZEBRA' & 'MOOSE' CONDUCTOR.

1.Specification to which the finished conductor conforms: IS-398Part-II-1976
2.Purity of Aluminium Rods: 99.5% Minimum
3.Percentages of Carbon in steel wire/rods: 0.50 to 0.85 (Preferably 0.65%)
4.Purity of Zinc: 99.95%

		Unit	ACSR 'Panther'	ACSR 'Zebra'	ACSR 'Moose'
5.	Particulars of Aluminium strands
i)	Diameter
	a) Standard	mm	3.00	3.18	3.53
	b) Maximum	mm	3.03	3.16	3.55
	c) Minimum	mm	2.97	2.19	3.51
ii)	Cross sectional area of standard diameter wire	mm2	7.069	7.942	9.787
iii)	Weight per Km
	a) Standard	Kg	19.11	21.47	26.45
	b) Maximum	Kg
	c) Minimum	Kg
iv)	Minimum breaking load
	a) Before stranding	KN	1.17	1.29	1.57
	b) After stranding	KN	1.11	1.23	1.49
v)	Maximum D.C. resistance at 200C	Ohm/Km	4.107	3.651	2.921
vi)	Joints in strands of 12 wire Aluminium layer if any		No joint	No joint	No joint
6.	Particulars of Steel strands
i)	Diameter
	a) Standard	mm	3.00	3.18	3.53
	b) Maximum	mm	3.06	3.21	3.60
	c) Minimum	mm	2.94	3.14	3.46
ii)	Cross sectional area of standard diameter wire	mm2	7.069	7.942	9.787
iii)	Weight per Km
	a) Standard	mm	55.13	61.95	76.34
	b) Maximum	mm	57.36	63.12	79.39
	c) Minimum	mm	52.95	60.40	73.33
iv)	Minimum breaking load
	a) Before stranding	KN	9.29	10.43	12.85
	b) After stranding	KN	8.83	9.91	12.22
v)	Elongation of 200 mm length on breaking	%	4	4	4
vi)	Coating of steel core
	a) Quality of Zinc		99.95% purity	99.95% purity	As per IS: 209-1979
	b) Process of galvanising		Hot Dip	Hot Dip	Hot Dip
	c) Minimum weight of coating	gm/m2	240	250	260
	d) Minimum no of dips of one minute duration which the strand can withstand (under preace test)	Nos.	3	3	3
7.	Particulars of Complete Conductor
i)	Code words, if any		ACSR 'Panther'	ACSR 'Zebra'	ACSR 'Moose'
ii)	Copper equivalent Area	mm2	310	260	325
iii)	Nominal aluminium area	mm2	200	420	520
iv)	Sectional area of aluminium	mm2	212.10	428.91	528.50
v)	Total sectional area	mm2	261.50	484.50	597.00
vi)	Overall diameter	mm	21.00	28.62	31.77
vii)	Stranding, lay and wire diameter
	a) Aluminium	mm	30/3.00 Right Hand lay	54/3.18	54/3.53
	b) Steel	mm	7/3.00	7/3.18	7/3.53
viii)	Lay ratio	Min. mMaxm
	a) Steel core
	i) 6 wire Layer	Max.	28	28	28
		Min.	13	13	16
	b) Aluminium
	i) 12 Wire Ist Layer	Max.	16	15	14
		Min.	10	10	12
	ii) 18 Wire IInd layer	Max.	14	14	13
		Min.	10	10	11
	iii) 24 Wire IIIrd Layer	Max.	-	12	12
		Min.	-	10	10
x)	Approximate calculated breaking load	KN	89.67	130.32	159.60
xi)	Final modules of Elasticity (Practical)	GN/m2	80	69	69
xii)	Coefficient of linear expansion	Per0C	17.8x10-6	193x10-6	19.35x10-6
xiii)	Approximate total weight per Km
	a) Steel Section	Kg	388.00	437.00	537.00
	b) Aluminium Section	Kg	586.00	1184.00	1461.00
	c) ACSR Composite	Kg	974.00	1621.00	1998.00
xiv)	Calculated D.C. resistance at 200C (Maximum)	Ohm/Km	0.1390	0.06885	0.25595
xv)	Standard length of conductor (with tolerance, if any)	Metres	1500+5%	1500+5%	1500+5%
xvi)	Number of standard length in one reel (drum)	Nos	One	One	One
xvii)	Random lengths (Maximum percentage of the lengths ordered)	%	10	10	10